The ultimate objective of the research projects in this application is to improve our understanding of how a variety of factors interact in generating normal hematopoiesis or in generating leukemia. Many of the proposed experiments involve manipulating the mouse strain, and conducting experiments in which the mice are observed over time for development of leukemia. It is anticipated that the results of these four projects will inform one another. Project results will be conveyed to other members of the program with the assistance of members of the Biostatisticas Core. The Biostatistics Core will assist all the research projects contained in this program. The purpose of the Biostatstics Core, is to provide the following services that will be utilized by the research proj ects included in this Program Project. 1. To provide biostatistical collaboration for animal studies, including the laboratory components of those studies. This will include all aspects of the design and analysis of such studies. 2. To provide biostatisticat support for the microarray studies of Project 4.